Process of vulcanizing rubber and product obtained thereby



Patented Nov. 23, 1943 PROCESS OF VULCANIZING RUBBER AND PRODUCT OBTAINED THEREBY Marion W. Harman, Nitro,

W. Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a

corporation of Delaware No Drawing. Application February 17, 1940, Serial No. 319,499

16 Claims.

The present invention relates to a new class of rubber vulcanization accelerators and to the vulcanization of rubber by an improved process wherein there is employed a preferred class of compounds in the vulcanization process and to the vulcanized rubber products so obtained.

This invention comprises the use of tertiary cyclohexylamine salts in the vulcanization process and is a continuation in part of my co-pending application, Serial No. 198,112, filed March 25, 1938, now U. S. 2,223,446. The new accelerators have been found to accelerate the vulcanization of rubber but it is preferred to employ them in conjunction with other organic accelerators, particularly thiazole accelerators whereby rubber products exhibiting improved properties are obtained.

' As examples of tertiary cyclohexylamine salts of this invention there may be mentioned dimethyl cyclohexylamine oleate, dimethyl methyl cyclohexylamine oleate, dimethyl cyclohexylamine stearate, dimethyl cyclohexylamine palmitate, dimethyl cyclohexylamine myristate and dimethyl cyclohexylamine naphthenate but preferably salts of aromatic carboxylic acids as for example dimethyl cyclohexylamine benzoate, di methyl cyclohexylamine salicylate, diethyl cyclohexylamine benzoate, dimethyl cyclohexylamine phthalate and di(dimethyl cyclohexylamine) phthalate. This last mentioned compound has been found to be particularly efiicacious due to its nondiscoloring of the cured rubber products and further, although activating thiazole accelerators to a surprising degree has little tendency to scorch or pre-vulcanize the rubber during processingj U Salts of the class exemplified above are readily obtainable by mixing the proper molecular proportions of the amine with the organic acid.

Where convenient or desirable, the reaction may be enhanced by the application of heat, the use of solvents and the like. For'example 49.8 parts by weightisubstantially 0.3 molecular proportion) of phthalic acid were dissolved in alcohol and to the solution so prepared N,N dimethyl cyclohexylamine was'added in an amount somewhat in excess of the calculated quantity for forming di(N,N dimethyl cyclohexylamine) phthalate. The temperature of the alcohol solution was maintained at substantially 50-70 dur--- ing the addition. After completion of the reaction the alcohol was evaporated and the white crystalline} residue extracted with petroleum ether to remove the excess of amine leaving the desired di(N,N dimethyl cyclohexylamine) phthalate which melted at 136-139 C.

As exemplary of the preparation of a salt of a fatty acid 70.5 parts by weight of oleic acid (substantially 0.25 molecular proportion) were dissolved in alcohol in a suitable container and heated to refluxing, at which temperature a solution in alcohol of 30.5 parts by weight (substantially 0.25 molecular proportion) of dimethyl cyclohexylamine were added thereto. Heating was continued until the reaction was complete and the solvent then removed leaving the desired salt as a liquid residue.

While specific preparations of the preferred class of materials have been described above, other methods of preparation may be utilized Where convenient or desirable. It is to be understood therefore that these preparations are not limitative of the invention but illustrative thereof.

As a specific embodiment of the invention showing the use of the new class of materials as accelerators for the vulcanization of rubber but which again are intended to illustrate the invention and not to limit the same, rubber stocks were compounded comprising- Stock Parts by Parts by weight weight Pele crepe rubber 100 100 Zinc oxide. 10 10 3 3 0. 5 0. 6

testing the cured rubber products:

Table I Modllgus of elasticity Cure a e onga' Tensile at Ult. Stock time in nous brealg, in elong.,

minutes lbs./1.11. per cent A; 60 90,. 240 800 960 B 60 I 425 1, 416 3, 835 A 90 315 1, 240 990 B 90 430 V 1, 340 2, 75 0 825 The above data show the desirable accelerating propertiesof the preferred class of compounds. It is preferred, however, to employ them in conjunction with other organic accelerators whereby new and improved results in the vulcanization of rubber are obtained. Thus the new compounds show a desirable activation of other organic accelerators when employed in conjunction therewith and produce vulcanized rubber products possessing excellent modulus and tensile properties but without the disadvantage usually accompanying accelerator activation of small amount "of one :of the preferred class materials to a thiazole accelerator, for example 75 capto .thiazoles.

scorch or prevulcanization. In addition the salts of the higher fatty acids, for exampleithose containing from ten to twenty carbon atoms in the molecule, exhibit desirable softening of the uncured rubber stocks so that less time and power is consumed in the milling :or similar operation. The usual accelerators commonly employed commercially may be used in conjunction with the 4 new compounds of this inventionas'for example thiazole accelerators such as mercaptobenzothia- I zole, mercapto phenyl benzothiazole, mercapto naphtha thiazole, mercapto ,methylithiazole and mercapto methyl benzothiazole. include by the term mercapto thiazole" accelerators reaction products of mercapto thiazoles .as well as the free mercapto :thiazole. Further --examples :are organic base greaction products ,of

-dehy de amines may the-employed, :specific examples of which :are sodium :dimethyl ithiocar- 'bamate, :tetra methyl thiuram "disulfide, piperi- :dine :cyclopentamethylene :dithiocarbamate, bu-

tyzlaldehyde ganiline, i-acetaldehydeeaniline and formaldehyde-aniline.

Theo-following are examples of the preferred embodiment of :the invention showing ,the use of the new compounds jnconjunction with gthiazole accelerators .but rare in onorwise .limitative .of .the 3 invention.

Rubber stocks were compounded comprising- Stock Zinc oxlde Sulfur" 3 Stearic aci 0.5 i

ercaptobenzothiazolc 0. 75 75 0. 75 rDi(N,Ndimethyl'cyclohexylamine) phthalate 0. 0.

The stocksso compounded were ,vulcanizedby heating in a press at 'the temperature 0f twenty pounds of steam pressure per square inch and the .following modulus ,and tensile properties obtained p n testing the cured rubber products.

Table 'II Modulus of :elasticity Cure "i ig -gfi Tensilezat Ult. Stock time in break, in elong,

:unmutes lbs/in? perpent 15 130 310 1, 560 l, 015 015' 5225 ;82.0 "2,260 900 .15 ,310 1,120; 2,650 855 p "270 860 2, '120 "870 '30. 455 1,790 3, 390 1820 30 :555 2, 200 J .800 45; 360 1; 200 2; 930 865 :45 :625 2,520 B, 880 L800 45 720 .2, 740 4,100 775 440 l, 460' 3; 015 825 "90. F725 2790 14,000 770 ,90 820 3, 030 3, 720 735 The above data show that the addition of a It is meant :to

mercaptobenzothiazole, gives a faster curing and a higher modulus and tensile stock.

The following is further exemplary of the preferred embodiment of the invention. Rubber stocks were compounded comprising- Stock I F 1 G Parts by Parts by weight weight Pale creperubber i 100 111 L1 i i 3 3 Zinc oxide t 5 5 Stcaric-am 1 l Di(benzothiazyl thiol) dlmcthyl urea 0. 6 0i 0 N,N di1nethyl,cyclohexylamineoleatc 0.1 Di(-N;N dimethyl cyclohcxylamine) p thal 1 te i. t.4. v .7 0.

Table III Modulus of elasticity mlbsjim at elonga Tensile It tions 0fat break,

V in ,elong., lbs/in? Percent 500% 700% 200 670 12,000 880 280 1, 080 12, 500" 830 320 mm 2,080- 305 405 l,'760 7 2,075 790 385; 1,010 2,800 795 1455 ;2, 000 3,235 780 525 2, 3,250 770 080" 2,310. 3,2075 740 The above data show the desirable modulus and tensile properties obtained by the :use of a tertiary cyclohexylamine salt of anorganic carboxylic acid in conjunction with an organic base reaction product of a mercapto thiazole.

As further specific embodiments of this-invention a-rubberstock was compounded comprising {The-stock so compounded wasvulcanized by heating in :a press at the temperature of twenty ounds :of steam ;,pressur e per {square inch. The

hysical properties ;of the cured rubber products tarehown below:

Table IV ;M odulus of elasticity."

uglbs'lmz'at elonga' Tensile at Ult.

Quretlmeinmlnutes tmnsof" v'm.-eak,.in clung 'lbsJinfl per cent The above data further :show the desirable modulus and tensile properties obtained by use of the preferred class of materials in conjunction with organic vbase reaction products of mer- The new and preferred class of materials may be employed with other accelerators than those specifically mentioned. This invention is not restricted to the use of the particular compounds given in the disclosure as examples nor is it re stricted to their use in the particular rubber mixes herein described but this invention is limited only by the claims attached hereto as part of the present specification.

What is claimed is:

1. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of an N, N dialkyl cyclohexylamine salt of an organic carboxylic acid selected from the group consisting of higher fatty acids containing at least ten carbon atoms and aromatic carboxylic acids.

2. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of an N, N dimethyl cyclohexylamine salt of an aromatic carboxylic acid.

3. The processs of vulcanizing mbber which comprises heating rubber and sulfur in the presence of an N, N dimethyl cyclohexylamine salt of phthalic acid.

4. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of an N, N dimethyl cyclohexylamine salt of a fatty acid containing at least ten but less than twenty carbon atoms.

5. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of an N, N dimethyl cyclohexylamine salt of an aromatic carboxylic acid containing a single benzene nucleus in the presence of an organic accelerator of a different class.

6. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of an N, N dialkyl cyclohexylamine salt of an organic carboxylic acid selected from the group consisting of higher fatty acids containing at least ten carbon atoms and aromatic carboxylic acids in the presence of a thiazole accelerator.

7. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of di(N, N dimethyl cyclohexylamine) phthalate.

8. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of N, N dimethyl cyclohexylamine oleate.

9. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of an N, N dialkyl cyclohexylamine salt of an organic carboxylic acid selected from the group consisting of higher fatty acids containing at least ten carbon atoms and aromatic carboxylic acids.

10. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of an N, N dimethyl cyclohexylamine salt of an aromatic carboxylic acid.

11. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of an N, N dimethyl cyclohexylamine salt of phthalic acid.

12. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of an N, N dimethyl cyclohexylamine salt of a fatty acid containing at least ten but less than twenty carbon atoms.

13. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of an N, N dimethyl cyclohexylamine salt of an arcmatic carboxylic acid containing a single benzene nucleus in the presence of an organic accelerator of a different class.

14. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of an N, N dialkyl cyclohexylamine salt of an organic carboxylic acid selected from the group consisting of higher fatty acids containing at least ten carbon atoms and aromatic carboxylic acids in the presence of a thiazole accelerator.

15. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of di(N, N dimethyl cyclohexylamine) phthalate.

16. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of N, N dimethyl cyclohexylamine oleate.

MARION W. HARMAN. 

